1. Field of the Invention
This invention relates to the field of color image processing apparatuses, such as digital copying machines or color facsimile machines, and in particular relates to an apparatus which discriminates an image characteristic using image signals obtained by scanning an original document.
2. Description of the Related Art
A color image processing apparatus, such as a digital copying machine or a color facsimile machine, which optically reads an original document image by an image scanner, and obtains a color image signal represented using red, green, and blue (RGB) signals for each pixel, processes the image signals, and prints the color image using colorants of cyan, magenta, yellow, and black (CMYK) is well known.
Generally, the original document includes many image regions, such as a photographic image region, a gray scale image region, a half tone image region, a binary text image region, and so on. Therefore, in the color image forming apparatus, it is important to perform appropriate signal processing with respect to each characteristic of the image region in the original document image. For this reason, the image processing apparatus discriminates characteristics of the inputted image signals obtained by the image scanner.
However, it is difficult to obtain the exact same result of image discrimination for each scan of an original document using the present technology. In other words, there will be differences in each scan due to the accuracy of the image scanner. This generates noise or a stain in the printed image even in a small area. For example, the color image processing apparatus should provide only black colorant for an edge region in a black character image or a black edge portion in a picture image, so as to obtain high quality printing. If there is a mistake in the discrimination result concerning each scan of a document image, a stain of black colorant in the edge region of the black character image would occur because another colorant would be mixed in the black edge region.
To overcome the above mentioned problems, an image processing apparatus is disclosed in U.S. Pat. No. 5,189,523, which is hereby incorporated by reference. The image processing apparatus includes a bit map memory with an address counter for storing the image discrimination results. The apparatus provides a pre-scan, that is, an additional image scan before the image forming operation starts, and stores the image discrimination result in the bit map memory with respect to each pixel. Then, the apparatus assesses the image forming operation to provide the appropriate processing after a next scanning for forming the image. Accordingly, it is possible to use the same discrimination result in each image forming operation with respect to C, M. Y, and K colorants.
However, the conventional apparatus requires a large amount of bit map memories for storing the image discrimination results with respect to each pixel. An example of a memory amount required to store a discrimination result in the bit-map memory is as follows:
Document Size: A4 (297 mm.times.210 mm) PA1 Input Pixel Density: 16 dots per mm PA1 Memory Amount: (297.times.16).times.(210.times.16)=15966720 bits
The above mentioned memory amounts, approximately 16 megabyte, would be provided for each discrimination result in the conventional image processing apparatus. Therefore, the amount of memory required to provide an image processing apparatus which generates high quality images cannot be achieved at a reasonable cost.